Immobilization of Escherichia coli Cells Containing Aspartase Activity with Polyurethane and Its Application for l -Aspartic Acid Production

Abstract

Whole cells of Escherichia coli containing aspartase activity were immobilized by mixing a cell suspension with a liquid isocyanate-capped polyurethane prepolymer (Hypol). The immobilized cell preparation was used to convert ammonium fumarate to l -aspartic acid. Properties of the immobilized E. coli cells containing aspartase were investigated with a batch reactor. A 1.67-fold increase in the l -aspartic acid production rate was observed at 37°C as compared to 25°C operating temperature. The pH optimum was broad, ranging from 8.5 to 9.2. Increasing the concentration of ammonium fumarate to 1.5 M from 1.0 M negatively affected the reaction rate. l -Aspartic acid was produced at an average rate of 2.18 × 10 −4 mol/min per g (wet weight) of immobilized E. coli cells with a 37°C substrate solution consisting of 1.0 M ammonium fumarate with 1 mM Mg 2+ (pH 9.0).